Field of the Disclosure
Embodiments of the present disclosure relate to the art of a control system for a hybrid vehicle in which a prime mover includes an engine and a motor.
Discussion of the Related Art
JP-A-2017-007437 describes a drive unit for a hybrid vehicle comprising a first planetary gear unit and a second planetary gear unit. According to the teachings of JP-A-2017-007437, the first planetary gear unit comprises a first carrier connected to an engine, a first sun gear connected to a motor, and a first ring gear. The second planetary gear unit comprises a second carrier rotated integrally with the first ring gear, a second sun gear, and a second ring gear as an output member. The first carrier and the second sun gear are selectively engaged to each other by a first clutch, the second sun gear and the second ring gear are selectively engaged to each other by a second clutch, and a brake torque is applied to the first carrier by a brake. The hybrid vehicle taught by JP-A-2017-007437 can be propelled in an Electric Vehicle mode while stopping the engine by engaging the brake and any one of the first clutch and the second clutch.
According to the teachings of JP-A-2017-007437, a ratio of a speed of the first sun gear (i.e., a motor speed) to a speed of the second ring gear (i.e., an output speed) becomes greater in the EV mode in which the first clutch is engaged, in comparison with that in the EV mode in which the second clutch is engaged. In other words, during propulsion in the EV mode at a predetermined speed, the motor speed is raised higher by engaging the second clutch rather than engaging the first clutch. That is, in the EV mode, a speed reducing ratio is increased by engaging the second clutch.
In addition, according to the teachings of JP-A-2017-007437, the engine can be started by generating a torque by the motor in a direction to reduce the motor speed while releasing the brake. Consequently, the motor generates an electric power.
That is, according to the teachings of JP-A-2017-007437, the motor generates larger amount of electricity when cranking the engine in the EV mode while engaging the second clutch. However, if the engine is started during propulsion in the EV mode while engaging the second clutch at a high speed, an excessive electrical input may be applied to a battery, and hence the battery may be damaged.